Method and system for producing a precured tread strip

ABSTRACT

A method and system for producing a precured tread strip, whereby a rubber mixture is extruded into a continuous tread strip, from which the precured tread strip is detached; the bottom surface of the precured tread strip is buffed, and the precured tread strip then inserted inside a bag made of material impermeable to air and which is then sealed; and a vacuum is formed inside the bag just before the bag containing the precured tread strip is sealed.

CROSS-REFERENCE

This applications claims priority from Italian Patent Application No. T002006A000102, Filed Feb. 14, 2006.

The present invention relates to a method and system for producing a precured tread strip.

The present invention may be used to advantage in cold retreading of truck tyres, to which the following description refers purely by way of example.

BACKGROUND OF THE INVENTION

Cold retreading of a truck tyre normally comprises removing the worn tread from the tyre carcass; and applying a new tread to the tyre carcass by winding an intermediate strip of green rubber and a molded, precured tread strip about the carcass, and then put the carcass inside an autoclave for further curing to ensure optimum adhesion of the tread to the carcass by virtue of the bonding action of the intermediate strip.

One example of a precured tread strip ready for application to a tyre carcass is described in U.S. Pat. No. 5,277,727A1; and one example of a tyre retreading station using the above method is described in U.S. Pat. No. 6,368,439B1.

The precured tread strips are produced by producing a green-rubber mixture; extruding the green-rubber mixture to form a continuous strip of green tread; cutting the continuous strip of green tread transversely into green tread strips of given length; and then curing each green tread strip.

At this point, the bottom surface of each precured tread strip is “buffed”, i.e. brushed and/or abraded to remove any rubber-metal nonstick surface agents remaining after the curing process, to increase the specific surface area, and so improve adhesion to the carcass; and, finally, the precured tread strip is rolled up for transfer to the retread station.

Oxygen in the air has been found to produce surface oxidation, and so impair grip, of the bottom surface of the precured tread strip. To protect the bottom surface of the precured tread strip from oxidation, it is therefore common practice to spray the bottom surface with a coating of liquid (so-called “cement”) containing green rubber and normalheptane (or other organic solvent), and which, in addition to protecting the bottom surface of the precured tread strip against oxidation, also assists adhesion of the precured tread strip to the intermediate strip of green rubber between the precured tread strip and the carcass for retreading. It should be pointed out that, the “cement” being adhesive, a sheet of plastic material must be placed on the bottom surface of the “cemented” precured tread strip before it is rolled up.

Sample tests of retreaded tyres, however, show adhesion of the new tread to the retreaded tyre carcass to be frequently poor, thus at least partly impairing performance, though without actually impairing the safety of the retreaded tyre.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and system for producing a precured tread strip, designed to eliminate the aforementioned drawbacks and which, in particular, are cheap and easy to implement.

According to the present invention, there are provided a method and system for producing a precured tread strip, as recited in the attached Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows, schematically, a system for producing a precured tread strip in accordance with the present invention;

FIG. 2 shows, schematically, a sequence of packing operations performed at a packing station of the FIG. 1 system;

FIG. 3 shows, schematically, an alternative sequence of packing operations performed at the packing station of the FIG. 1 system;

FIG. 4 shows, schematically, a further sequence of packing operations performed at the packing station of the FIG. 1 system.

DETAILED DESCRIPTION OF THE INVENTION

Number 1 in FIG. 1 indicates as a whole a system for producing precured tread strips 2 for cold retreading truck tyres.

System 1 comprises a mixing device 3 for producing a green-rubber mixture, which is fed to an extruding device 4 where the green-rubber mixture is extruded into a continuous strip 5 of green tread. Downstream from extruding device 4, a cutting device 6 cuts the continuous strip 5 of green tread into a succession of green tread strips 2 of given length; downstream from cutting device 6, a curing device 7 cures green tread strips 2; and, downstream from curing device 7, a trimming device 8 preferably removes the curing flashes from each precured tread strip 2.

Downstream from trimming device 8, a buffing device 9 buffs the bottom surface 10 of each precured tread strip 2. More specifically, buffing comprises brushing and/or abrading the bottom surface 10 of each precured tread strip 2 to remove any rubber-metal nonstick surface agents remaining after the curing process, to increase the specific surface area and so improve adhesion to the intermediate strip of green rubber applied about a respective carcass of a tyre for retreading.

As soon as bottom surface 10 of precured tread strip 2 is buffed, each precured tread strip 2 is vacuum packed inside a bag 12, made of shockproof, heat-seal plastic material impermeable to air (e.g. polyethylene), at a packing station 11 downstream from buffing device 9. More specifically, packing station 11 comprises an inserting device for inserting each precured tread strip 2 inside bag 12; a suction device for producing a vacuum inside bag 12 containing precured tread strip 2; and a sealing device for sealing bag 12 containing precured tread strip 2.

System 1 preferably also comprises a rolling device 13 for rolling each precured tread strip 2 up into a roll 14 for fast, easy storage and transport of precured tread strip 2. Each roll 14 is preferably stabilized by applying a non-adhesive belt 15 about roll 14.

In FIG. 2, rolling device 13 is located upstream from packing station 11, so that roll 14 is inserted inside bag 12. In FIG. 3, rolling device 13 is located downstream from packing station 11, so that a flat precured tread strip 2 is inserted inside bag 12, and the precured tread strip 2 and bag 12 containing precured tread strip 2 are subsequently rolled up together into roll 14.

Inserting roll 14 inside bag 12 to some extent complicates system 1, but on the other hand simplifies actual use of precured tread strip 2 on retread systems, which are currently designed to employ a precured tread strip 2 in the form of a roll 14 as opposed to a flat precured tread strip 2. Conversely, inserting a flat precured tread strip 2 inside bag 12 simplifies system 1, but, on existing retread systems, precured tread strip 2 in the form of roll 14 must be unrolled to remove bag 12 and then rolled back up into roll 14.

To eliminate any trace of oxygen inside bag 12, a feed device may be provided upstream from the suction device to feed an inert gas (typically nitrogen) inside bag 12 just before the vacuum is formed. It should be stressed that using inert gas to eliminate any trace of oxygen inside bag 12 is purely optional, in that vacuum sealing of bag 12 in itself ensures a very low residual oxygen level inside bag 12.

As shown in FIGS. 2 and 3, insertion of each precured tread strip 2 inside bag 12 comprises unwinding a strip 16 of tubular packing material off a reel 17; inserting precured tread strip 2 inside strip 16 of packing material; sealing bag 12 along strip 16 of tubular packing material by means of two transverse seals on opposite sides of precured tread strip 2; and detaching bag 12 from the continuous strip 16. Bag 12 is normally detached from strip 16 of packing material simultaneously with one of the two transverse sealing operations.

As shown in FIG. 4, inserting each precured tread strip 2 inside bag 12 comprises unwinding a strip 16 of flat packing material off a reel 17 (not shown); placing precured tread strip 2 on strip 16 of flat packing material; folding strip 16 of packing material into a tube about precured tread strip 2; stabilizing the tubular shape of strip 16 of packing material by means of a longitudinal seal; sealing bag 12 along strip 16 of packing material, folded into a tube about precured tread strip 2, by means of two transverse seals on opposite sides of precured tread strip 2; and detaching bag 12 from the continuous strip 16. Bag 12 is normally detached from strip 16 of packing material simultaneously with one of the two transverse sealing operations.

In one embodiment, system 1 may comprise a boxing device located downstream from packing station 11 to insert each roll 14 (or a group of rolls 14) inside a cardboard box.

Each molded, precured tread strip 2 leaving system 1 has no cement, and is enclosed in a vacuum-sealed bag 12 of material impermeable to air. It is important to note that system 1 as described above in no way involves “cementing” bottom surface 10 of precured tread strip 2, which is substantially protected against oxidation by the extremely low oxygen level inside vacuum-sealed bag 12.

The above method of inserting each precured tread strip 2 inside a respective bag 12 sealed immediately after bottom surface 10 is buffed, and with no “cementing” (i.e. application of an organic solvent with added rubber), has numerous advantages.

Tests of tyres retreaded with precured tread strips 2 packed inside sealed bags show a high degree of adhesion between the new tread and the underlying carcass.

Moreover, organic solvents being highly pollutant, eliminating application of organic-solvent-based “cement” provides for greatly reducing overall pollution of the precured tread strip 2 manufacturing process. In this connection, it is important to note that recent European Union standards (VOC 13/1999/ECV) call for a 75% reduction in the use of organic solvents in industrial processes by the year 2007. 

1) A method of producing a precured tread strip (2); the method comprising the steps of: forming a rubber mixture; extruding the rubber mixture into a continuous tread strip (5); detaching the precured tread strip (2) from the continuous tread strip (5); and buffing a bottom surface (10) of the precured tread strip (2); the method is characterized by comprising the further steps of: inserting the precured tread strip (2) inside a bag (12), made of material impermeable to air, immediately after buffing the bottom surface (10) of the precured tread strip (2); forming a vacuum inside the bag (12) containing the precured tread strip (2); and sealing the bag (12) containing the precured tread strip (2). 2) A method as claimed in claim 1, wherein the precured tread strip (2) is rolled up into a roll (14). 3) A method as claimed in claim 2, wherein the roll (14) is stabilized by applying a belt (15) about the roll (14). 4) A method as claimed in claim 2, wherein the precured tread strip (2) is rolled up into a roll (14) after the precured tread strip (2) is inserted inside the bag (12). 5) A method as claimed in claim 2, wherein the precured tread strip (2) is rolled up into a roll (14) before the precured tread strip (2) is inserted inside the bag (12). 6) A method as claimed in claim 1, wherein inert gas is fed into the bag (12) before the vacuum is formed. 7) A method as claimed in claim 6, wherein the inert gas is nitrogen. 8) A method as claimed in claim 1, wherein the bag (12) is made of heat-seal polyethylene. 9) A method as claimed in claim 1, wherein the step of inserting the precured tread strip (2) inside the bag (12) comprises: unwinding a strip (16) of tubular packing material, impermeable to air, off a reel (17); inserting the precured tread strip (2) inside the strip (16) of tubular packing material; sealing the bag (12) along the strip (16) of tubular packing material by means of two transverse seals on opposite sides of the precured tread strip (2); and detaching the bag (12) from the strip (16) of packing material. 10) A method as claimed in claim 1, wherein the step of inserting the precured tread strip (2) inside the bag (12) comprises: unwinding a strip (16) of flat packing material, impermeable to air, off a reel (17); placing the precured tread strip (2) on the strip (16) of packing material; folding the strip (16) of packing material into a tube about the precured tread strip (2); stabilizing the tubular shape of the strip (16) of packing material by means of a longitudinal seal; sealing the bag (12) along the strip (16) of packing material, folded into a tube about the precured tread strip (2), by means of two transverse seals on opposite sides of the precured tread strip (2); and detaching the bag (12) from the strip (16) of packing material. 11) A method as claimed in claim 1, wherein the precured tread strip (2) is cured immediately after the precured tread strip (2) is detached from the continuous tread strip (5). 12) A system (1) for producing a precured tread strip (2); the system (1) comprising: a mixing device (3) for producing a rubber mixture; an extruding device (4) for extruding the rubber mixture into a continuous tread strip (5); a cutting device (6) for cutting the precured tread strip (2) from the continuous tread strip (5); and a buffing device (9) for buffing a bottom surface (10) of the precured tread strip (2); the system (1) is characterized by comprising a packing station (11) located downstream from the buffing device (9) and in turn comprising: an inserting device for inserting the precured tread strip (2) inside a bag (12), made of material impermeable to air, immediately after the bottom surface (10) of the precured tread strip (2) is buffed; a suction device for forming a vacuum inside the bag (12) containing the precured tread strip (2); and a sealing device for sealing the bag (12) containing the precured tread strip (2). 13) A system (1) as claimed in claim 12, wherein a rolling device (13) rolls the precured tread strip (2) up into a roll (14). 14) A system (1) as claimed in claim 13, wherein the rolling device (13) is located upstream from the packing station (11). 15) A system (1) as claimed in claim 13, wherein the rolling device (13) is located downstream from the packing station (11). 16) A system (1) as claimed in claim 12, wherein, upstream from the suction device, a feed device feeds an inert gas into the bag (12). 17) A system (1) as claimed in claim 12, wherein, upstream from the cutting device (6), a curing device (7) cures the continuous tread strip (5). 18) A molded, precured tread strip (2) for cold retreading a truck tyre; the precured tread strip (2) is characterized by having no cement, and by being enclosed in a vacuum-sealed bag (12) of material impermeable to air. 